The invention concerns a crane trolley, particularly one with a short overall height. The invention is particularly useful with a single-rail trolley having a running gear frame having a hoisting mechanism, which can travel by running wheels on a rail. The invention is illustrated with a crane trolley having a lower flange of an essentially horizontally situated beam, with at least one running wheel being driven, and on the underside of the rail is arranged a friction roller interacting with the driven running wheel.
In crane trolleys with short overall height, in order to accomplish a compact and space-saving construction, the hoisting mechanism is arranged at the side, next to the beam carrying the rail, so that the actual load lifting tackle—the load hook—can be lifted as high as possible underneath the beam. This arrangement of the hoisting mechanism next to the beam produces an off-center position of the center of gravity of the running gear frame relative to the center of the beam. Due to this off-center shifting of the center of gravity, there is a risk when operating without a payload that the running wheels arranged on the rail, especially the lower flange of a beam, will lift up relative to the hoisting mechanism.
Such lifting should be avoided in order to prevent damage to the crane trolley and/or beam and avoid a slippage of the driven running wheels.
Various solutions are known from practice for solving this problem. One variant is to arrange a counterweight on the side of the running gear frame opposite the hoisting mechanism, so as displace the center of gravity back to the middle of the beam. A counterweight, on the one hand, takes up additional space, and on the other hand the proper weight of the crane trolley and the load on the beam is needlessly increased.
Generic crane trolleys are known from DE 42 09 565 C2 and EP 0 620 179 B1, in which a friction roller interacting with at least one driven running wheel is arranged on the underside of the lower flange. This likewise driven friction roller can be forced by a spring mechanism against the underside of the lower flange, in order to increase the traction of the driven running wheel.
These designs used in familiar driven friction rollers are often cumbersome and take up space, due to the drive unit of the friction roller. Furthermore, the wear behavior of the interacting driven running wheels and friction rollers is normally different, so that the rolling radii change in different ways, which again results in additional slippage of the less loaded wheel.
U.S. Pat. No. 3,212,455 discloses a single-rail crane trolley in which a friction roller can be adjusted on the underside of the traveling rail opposite a running wheel in order to prevent an undesirable tilting. By adjusting a screw, the friction roller can be swiveled in order to adjust the distance between the particular running roller and itself to prevent a tilting depending on the traveling rail.